Fingerprints are impressions of the system of ridges on the finger surface. Most latent fingerprints, i.e., those hidden from the unaided eye, are formed when perspiration escapes through the ridged surface. Human perspiration is a mixture of many substances including fatty acids, proteins, peptides, amino acids, chloride salts, water, and urea.
Under present forensic science practices, the particular analytical technique used for fingerprint detection varies depending upon the type of substrate. For example, the typical process on a paper substrate involves application of ninhydrin (triketohydrindene hydrate) to the paper and allowing the print to develop by heating under high humidity. Ninhydrin is commonly used as a colourimetric reagent for determination of, e.g., amino acids (see The Condensed Chemical Dictionary, 10the Ed., Van Nostrand Reinhold Co., 1981).
Another process for detecting latent fingerprints on surfaces that have been exposed to water involves the use of a reagent known as physical developer (PD) or stabilized physical developer (SPD). This process uses a silver-based reagent typically including ferrous ammonium sulfate, ferric nitrate, silver nitrate, a citric acid buffer and one or more surfactants. One disadvantage in this process is that the substrate is generally soaked in a maleic acid solution as one step. Maleic acid presents mild handling problems. Another disadvantage is that the process uses a significant amount of silver per application as one batch uses about 20 grams (g) of silver nitrate and is useful for up to about forty runs or about two days. Thus, this process may use from about 0.5 g up to about 20 g of silver nitrate for each potential print depending on the number of runs.
Within the past decade, a process using the fumes of cyanoacrylate esters for the detection of latent fingerprints has also found widespread use on a range of substrates. Such esters are particularly useful on materials such as polystyrene. However, there are some problems with the toxicity of these materials.
Although numerous other fingerprint detection techniques have been developed, extensive research has continued over the past decade in the field of latent print detection. One difficulty has been in developing a technique usable to detect latent fingerprints found on a wide range of potential substrates.
Accordingly, it is an object of this invention to provide a widely usable method or technique for the detection and visualization of latent fingerprints.